1994 E320 AC woes - PeachParts Mercedes-Benz Forum

94E320Coupe · #1 03-18-2018, 03:01 PM

Hi all,

Car has 73K original miles.

Recently, AC selected- blows warm air. ( sudden onset )

Drove it home and parked it overnight.
When I started it the next day AC worked fine initially.

Shut off and restarted and back to blowing warm air.

Drove it around for about 30 minutes and returned home with no joy.

( OAT about 80 F )

Popped the bonnet and noticed that the aux fans are not coming on with AC selected and engine running sitting in the driveway. ( warm engine and warm outside )

So far, checked fuses ( aux fan and relay fuse ) and removed and re-plugged both relays.

Checked all connections and wiring that I could see, including thermostat, resistor and dryer connections.

Don't want to start throwing electrical parts at it until I narrow down the issue a bit.

Any troubleshooting help would be appreciated.

Rob in Austin TX

240diowa · #2 03-19-2018, 01:52 PM

It sounds like you may be low on freon such that the pressure switch is not activated. From car I have worked on in the past the pressure switch needs to be engaged to activate the aux fans and the compressor.

sixto · #3 03-19-2018, 10:18 PM

Might have a flaky evaporator temp sensor.

Sixto
98 E320s sedan and wagon

JimFreeh · #4 03-23-2018, 08:52 PM

What's the compressor clutch doing?

Jim

Diseasel300 · #5 03-24-2018, 09:52 AM

Quote:

Originally Posted by JimFreeh

What's the compressor clutch doing?

^^^x2

If you can see the clutch pull in and the compressor hub is rotating, throw a set of gauges on and see what your pressures look like. You have to be up ~250-300PSI on the high side before the electric fans kick on.

If the clutch is not engaging, you could have low pressure and the pressure switch is doing its job, Klima relay issues (assuming the '94 still has it), or issues with the pushbutton unit.